The present invention relates to a machine tool chuck of the type in which workpiece clamping pawls can be quickly slid out in the radial direction for replacement.
A known machine tool chuck of the type described above and disclosed in Japanese Patent Publication No. 63-15085 published Apr. 2, 1988 generally comprises a chuck main body, master jaws radially slidably fitted in the chuck main body, and workpiece clamping pawls radially slidably fitted in the chuck main body in opposing relationship with the master jaws, respectively, on the forward side of the body. Each master jaw has therein an axially slidable engaging member having on the forward face thereof rack teeth in mesh with rack teeth formed on the back surface of the corresponding workpiece clamping pawl. The engaging member can be moved in the axial direction by a radially shiftable operation pin in the master jaw. The master jaw is slidably engaged with an inclined groove of a wedge plunger. With the rack teeth of the engaging member maintained in mesh with the rack teeth of the clamping pawl, the wedge plunger is displaced in the axial direction of the chuck main body so that the clamping pawl is moved in the radial direction by the master jaw which is guided in the radial direction with high degree of accuracy. When the engaging member is axially retracted and its rack teeth are disengaged from the rack teeth of the clamping pawl, the pawl is released and can be slid in the radial direction for replacement.
In the known chuck of the type described above, in order to make the master jaw integral with the corresponding clamping pawl, the rack teeth of the master jaw are caused to engage with the rack teeth of the clamping pawl However due to errors which may occur from machining the engaging portions of the rack teeth, while replacing the clamping pawls, the positions in the radial direction of the replaced clamping pawls with respect to their corresponding master jaws tend to be slightly deviated so that the accuracy with which the chuck holds the workpiece becomes low.